Bob Graham is an old hand when it comes to writing policy tomes such as “Intelligence Matters: The CIA, the FBI, Saudi Arabia and the Failure of America’s War on Terror” and “America, The Owner’s Manual: Making Government Work for You.” But the latest effort by the former Florida senator and governor presents a different challenge — it’s fiction.

Out Tuesday, “Keys to the Kingdom” is a political thriller that takes readers on a journey that includes the murder of a former senator, nuclear weapons, a government cover-up and an ominously dangerous Saudi Arabia. POLITICO sat down with Graham, who left the Senate in 2005, to discuss how fictional his book really is.

Tell me about the book’s genesis.

It had several parents. One was anger. I co-chaired the congressional inquiry into Sept. 11, and I came away from that experience feeling there were some important questions for which there were answers, but there had been a cover-up to keep us from getting those answers. And part of this book is to try to provide some — albeit fiction, I think credible — answers to those questions.

Second, I had given a number of commencement addresses, and one of the standard lines was to stay alert and intellectually engaged, you ought to periodically challenge yourself to do something that is different than what you had done before and hard, such as learning a musical instrument or a new foreign language. And when I retired from the Senate in 2005, I thought I ought to eat my own cooking. So I decided that writing a novel would certainly be different, and it turned out to be really hard.

Tell me about the process of writing fiction and what challenges you perhaps hadn’t anticipated. Was it easier than nonfiction?

I’ve written three nonfiction books, and I found them to be easier in the sense that you already have a road map. … In a novel, you’ve got 300 blank pages; you can write whatever you are moved to put on paper. I found it to be a lot of fun writing a novel precisely because … you’ve got to come up with characters that are interesting and are affected by what happens in the book. You want your characters to be a different person at the end of the book, and that’s kind of fun.

Did you just literally sit down and start writing?

I wrote it in spurts, and then there were a couple of long delays. I was chairman of the weapons of mass destruction commission in 2008 and into 2009. I did almost no work on the novel during that period. And then, last year, I was co-chairman of the national oil spill commission, so I took an almost six-month sabbatical from the book. The WMD commission turned out to be very valuable to the novel because the plot is a terrorist group getting access to nuclear bombs, what the group would do with them, how affected they are and what the U.S. does to try to counter that. I did it all on the computer.

There’s a character — Tony Ramos — that you talk about at one point as the Will Smith of the State Department because of how he dresses. Is that based on a real person, and who is that person?

Most of the characters are composites. … Tony is probably the most composite-like. As someone who’s lived most of my life in south Florida, I know a lot of Cuban-Americans, so there are several people I have known who have contributed to this.

Do you feel that this book could only have been written by somebody with the kind of background in government and in your current capacities?

Immodestly, I don’t think there are very many people who could have written this book, because it requires some experiences that are not generally available, some understanding of the way the people in these positions function and some geopolitical understanding of international politics.

Was this enough to inspire you to write a second novel?

The publisher has asked me to write a second book, and if you get to the last chapter, it sort of presages the next book. I told the publisher I want to see how the first book is received before I commit to doing a second. But I hope there will be a second. … It will probably not be on nuclear terrorism, as this is, but on biological terrorism.

You’ve been such a prolific chronicler of your day-to-day activities (Graham has long kept a near-legendary personal diary of his daily life) … and that makes me think that you were an original tweeter, just before tweets existed. What is your take on modern social media and politicians?

I am not a tweeter. I think the difference is I do this for my personal records and it’s also reminders for things I have committed to do or want to do. It is not a public document. I have done about 2,500 of these, most of which, all except the last couple of years, are at a library at the University of Florida, and they will be at some time released to the general public. Now, they’re available on request for academics or for others who are interested. But it was not intended to be a form of communication, which Twitter is. I respect that, and I know a lot of people are interested in following the hour-by-hour activities of Paris Hilton and other prominent people, but that’s not what I’m about.